Abstract:

An acceleration sensor having a substrate, a first web that is connected
to the substrate, and a seismic mass that is fashioned as a frame and is
made up of four side frames, the first side frame and the third side
frame being situated opposite one another, the second side frame and the
fourth side frame being situated opposite one another, the second side
frame and the first web being connected via a first spring element,
stationary electrodes 50 being provided inside the frame that are
connected to the substrate, movable electrodes being provided that are
connected to the first side frame and/or to the third side frame, the
frame having a first transverse web that is connected to the first side
frame and to the third side frame.

Claims:

1. An acceleration sensor, comprising:a substrate;a first web that is
connected to the substrate;a first spring element;stationary
electrodes;movable electrodes; anda seismic mass that is fashioned as a
frame and is made up of four side frames, a first side frame and a third
side frame being situated opposite one another, a second side frame and a
fourth side frame being situated opposite one another, the second side
frame and the first web being connected via the first spring element, the
stationary electrodes being inside the frame that are connected to the
substrate, the movable electrodes being connected to at least one of the
first side frame and the third side frame;wherein the frame has a first
transverse web that is connected to the first side frame and to the third
side frame.

2. The acceleration sensor of claim 1, wherein the first web is inside the
frame, wherein a second web that is connected to the substrate is inside
the frame, and wherein a second spring element is connected to the fourth
side frame and to the second web.

3. The acceleration sensor of claim 1, wherein at least one of the second
side frame and the fourth side frame are fashioned at least partially as
a spring element.

4. The acceleration sensor of claim 3, wherein a bar is fashioned on at
least one of the spring element, the second side frame and the fourth
side frame, as a compensation for an etching environment.

5. The acceleration sensor of claim 1, wherein the first web has at least
one stop element that is allocated to at least one of the first side
frame, the third side frame, and the first transverse web as an abutment.

6. The acceleration sensor of claim 1, wherein the first transverse web is
adjacent to the first web.

7. The acceleration sensor of claim 2, further comprising:a second
transverse web that is adjacent to the second web.

8. The acceleration sensor of claim 7, wherein the stationary electrodes
and the movable electrodes are situated between the first transverse web
and the second transverse web, and wherein the movable electrodes are
connected to the first side frame and to the third side frame.

9. The acceleration sensor of claim 7, further comprising:a reinforcing
web that connects the first transverse web to the second transverse web.

10. The acceleration sensor of claim 9, wherein the reinforcing web is
connected to the movable electrodes.

11. The acceleration sensor of claim 9, wherein the reinforcing web is
fashioned as an electrode.

12. The acceleration sensor of claim 1, wherein two stationary electrodes,
having laterally offset fastening blocks, are situated between two
movable electrodes.

13. The acceleration sensor of claim 1, wherein at least one of the
following is satisfied: (i) the four side frames are at least partially
perforated; and (ii) the transverse webs are at least partially
perforated.

14. The acceleration sensor of claim 13, wherein the perforation has
rectangular slits.

15. The acceleration sensor of claim 1, wherein the frame has at least two
longitudinal elements situated alongside one another.

16. The acceleration sensor of claim 1, wherein the fourth side frame is
connected to the second web via a second spring element, and the second
web has stop elements that are provided as an abutment to the second
transverse web, and wherein stationary electrodes and movable electrodes
are situated between the first transverse web and the second transverse
web.

Description:

RELATED APPLICATION INFORMATION

[0001]The present application claims priority to and the benefit of German
patent application no. 10 2008 054 553.8, which was filed in Germany on
Dec. 12, 2008, the disclosure of which is incorporated herein by
reference.

FIELD OF THE INVENTION

[0002]The present invention relates to an acceleration sensor having a
substrate.

BACKGROUND OF THE INVENTION

[0003]Acceleration sensors are used for example to measure the
acceleration of the movements of vehicles. Acceleration sensors are
spring-mass systems in which, when accelerations occur, at least one
seismic mass is deflected relative to the substrate, against a reset
force that is capable of being modified with the deflection. The design
of acceleration sensors is based on the fact that they have both
electrodes connected to the seismic mass and electrodes connected to the
substrate, which may be fashioned as plate capacitors. During the
deflection caused by acceleration, a change in the electrical capacitance
can be measured between the electrodes connected to the substrate and the
electrodes connected to the seismic mass. The change in the capacitance
is acquired and evaluated using circuitry and makes it possible to
calculate the occurrent acceleration. For the manufacture of the
acceleration sensors, the mass and the springs are etched from silicon,
for example using a photolithographic process. In order to obtain a
self-supporting structure, a layer underneath the mass, for example of
silicon dioxide, is also removed by etching.

[0004]Such an acceleration sensor is discussed in German patent document
DE 10 2006 033 636 A1. The acceleration sensor includes a substrate, a
center web situated over the substrate, a first and second lateral web
situated at the sides of the center web, and a seismic mass, electrodes
being fashioned on the seismic mass and on the first and second lateral
web. In addition, the acceleration sensor has anchors that are situated
under the center web and under the first and second lateral web, and that
connect the center web and the two lateral webs to the substrate.

SUMMARY OF THE INVENTION

[0005]An object of the exemplary embodiments and/or exemplary methods of
the present invention is to provide an improved acceleration sensor that
has a compact arrangement and good mechanical stability.

[0006]The object of the exemplary embodiments and/or exemplary methods of
the present invention may be achieved by an acceleration sensor as
described herein. Further advantageous embodiments of the present
invention are also described herein.

[0007]The exemplary embodiments and/or exemplary methods of the present
invention has an acceleration sensor having a substrate, a first web
connected to the substrate, and a seismic mass. The mass is fashioned as
a frame and is made up of four sides, the first side frame and the third
side frame being situated opposite one another, and the second side frame
and the fourth side frame being situated opposite one another. The second
side frame and the first web are connected via a first spring element.
Inside the frame, stationary electrodes are provided that are connected
to the substrate. In addition, movable electrodes are provided that are
connected to the first side frame and/or to the third side frame. The
frame has a first transverse web that is connected to the first side
frame and to the third side frame.

[0008]An advantage of the acceleration sensor according to the present
invention is that the acceleration sensor has a stable or rigid
structure.

[0009]In a specific embodiment of the present invention, the first web and
a second web are provided inside the frame, the second web being
connected to the substrate. In addition, this specific embodiment has a
second spring element that is connected to the fourth side frame and to
the second web. This has the advantage that the acceleration sensor
according to the exemplary embodiments and/or exemplary methods of the
present invention is stable, and better use is made of the available
space.

[0010]According to another specific embodiment of the present invention,
the first web has at least one stop element that is allocated to the
first side frame, to the third side frame, and/or to the first
cross-section. An advantage of the stop element is that it ensures a
controlled maximum deflection.

[0011]In another specific embodiment of the present invention, stationary
electrodes and movable electrodes are situated between the first
transverse web and the second transverse web, the movable electrodes
being connected to the first side frame and to the third side frame. In
addition, a reinforcement web is provided that connects the first
transverse web to the second transverse web. This results in a structure
that improves the mechanical stability.

[0012]In addition, according to a further specific embodiment of the
present invention the acceleration sensor has a frame and a first and
second transverse web that are at least partly perforated. This has the
advantage that the first and second transverse web and the frame are
easily undercut, and thus can be safely separated from the substrate.

[0013]In another specific embodiment of the present invention, the second
web has stop elements that are provided as abutting elements on the
second transverse web. The advantage of this design is that the
acceleration sensor according to the present invention is given a desired
degree of stability.

[0014]In the following, the exemplary embodiments and/or exemplary methods
of the present invention is explained in more detail on the basis of
exemplary embodiments, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 shows a top view of the acceleration sensor according to the
present invention.

[0016]FIG. 2 shows a sectional view of the acceleration sensor according
to the present invention along the sectional line I-I of FIG. 1.

[0019]FIG. 5 shows a top view of a spring element, the fourth side frame
being fashioned as a spring element.

[0020]FIG. 6 shows, in a simplified representation, the acceleration
sensor according to the present invention, the webs and the spring
elements being situated outside the frame.

[0021]FIG. 7 shows another specific embodiment of a frame in an
acceleration sensor according to the present invention.

DETAILED DESCRIPTION

[0022]FIG. 1 shows a top view of an acceleration sensor. The acceleration
sensor is structured from a substrate 1, for example a silicon wafer. The
structuring can take place using known surface micromechanical methods.
Here, a mass and the springs are etched from the silicon as a
self-supporting structure using a photolithographic process. In order to
obtain a self-supporting structure, a layer of silicon dioxide situated
between the self-supporting structure and substrate 1 is also removed by
etching.

[0023]The acceleration sensor comprises a seismic mass that is fashioned
as a closed frame 2 and that is made up of four side frames 20, 21, 22,
23. First side frame 20 and third side frame 22, as well as second side
frame 21 and fourth side frame 23, are situated opposite one another, so
that frame 2 has a rectangular structure. In addition, frame 2 may be
partially perforated. The perforation makes it possible for an etching
medium to penetrate during the etching process to a layer that is
situated between frame 2 and substrate 1, so that frame 2 can be safely
separated from substrate 1.

[0024]Frame 2 has, as a perforation, a regular arrangement of
through-going slits 24. Slits 24 may have a rectangular shape and may be
centrically situated. First, second, third, and fourth side frames 20,
21, 22, 23 have slits 24 situated in the longitudinal direction.

[0025]The acceleration sensor has, in side frame 2, a first web 30 that is
connected to substrate 1. First web 30 is situated parallel to second
side frame 21 and is connected to second side frame 21 via a first spring
element 40. First spring element 40 is made up of three bearers 43.
However, more or fewer bearers 43 may also be joined to first spring
element 40, as long as these bearers have the same flexibility. In
addition, bearers 43 are situated parallel to second side frame 21.

[0026]Bearers 43 of first spring element 40 are connected or linked in end
areas by a spring linkage 42. Each spring linkage 42 has two linkages.
The linkage of bearers 43 to first web 30, or to second side frame 21,
takes place via a spring linkage 42 that is situated centrically and in
the longitudinal direction. In addition, two bearers 43 of first spring
element 40 are each linked at their outer end by a respective spring
linkage 42. Due to spring linkage 42, flexibility of first spring element
40 is ensured.

[0027]First web 30 has at least one stop element 7 that is allocated to
first side frame 20, to third side frame 22, and/or to a first transverse
web 60 as an abutment. The specific embodiment has a total of five stop
elements 7, one stop element 7 each being situated on first side frame 20
and on third side frame 22, and three stop elements 7 being situated on
first transverse web 60. However, more or fewer stop elements 7 may be
provided. In addition, pairs of stop elements 7 may be provided, the
first paired piece being situated on first web 30 and the second paired
piece being situated for example on first side frame 20, on third side
frame 22, and/or on first transverse web 60. Stop elements 7 limit the
deflection of frame 2 in the two main directions.

[0028]First transverse web 60 is provided adjacent to first web 30, and is
connected to first side frame 20 and to third side frame 22. In addition,
first transverse web 60 is situated parallel to web 30 and is fashioned
as a part of frame 2. Like frame 2, first transverse web 60 may be at
least partially perforated, i.e. first transverse web 60 may have a
regular arrangement of through-going slits 24. Slits 24 have a
rectangular shape and are situated centrically and in the longitudinal
direction of first transverse web 60. Due to the perforation, first
transverse web 60 can be reliably separated from substrate 1 during an
etching process.

[0029]A second transverse web 61 is situated parallel to fourth side frame
23. Second transverse web 61 is connected to first side frame 20 and to
third side frame 22. Like first transverse web 60, second transverse web
61 may be at least partially perforated, and can thus reliably be
separated from substrate 1 during an etching process. Second transverse
web 61 is provided adjacent to a second web 31.

[0030]Alternatively to the perforation shape shown in FIG. 1, the slits
(24) of the four side frames (20, 21, 22, 23) and/or of the transverse
webs (60, 61) may have a modified orientation and shape. For example, the
slits (24) may have an elliptical or quadratic shape, and may be situated
in the transverse direction. In addition, the slits (24) may have hole
perforations. In addition, there is the possibility that the four side
frames (20, 21, 22, 23) and/or the transverse webs (60, 61) are made up
of two or more longitudinal elements (11) situated alongside one another,
as shown in FIG. 7. Here, one or more longitudinal elements (11) have
perforations.

[0031]Second web 31 is situated between second transverse web 61 and
fourth side frame 23. Second web 31 is situated parallel to second
transverse web 61 and has at least one stop element 7 that is allocated
to first side frame 20, to third side frame 22, and/or to second
transverse web 61 as an abutment. In addition, pairs of stop elements 7
are respectively provided.

[0032]Second web 31 is connected to fourth side frame 23 via a second
spring element 41. The second spring element is made up of three bearers
43. In addition, bearers 43 are situated parallel to fourth side frame
23. Via spring linkage 42, bearers 43 of second spring element 41 are
connected to second web 31 or to fourth side frame 23. The linkage is
situated centrically and in the longitudinal direction of second spring
element 41. In addition, two bearers 43 of second spring element 41 are
each linked at the outer end by a respective spring linkage 42.

[0033]This design of the acceleration sensor has the advantage that a
compact construction is ensured and the acceleration sensor is given a
desired degree of stability.

[0034]First transverse web 60 and second transverse web 61 are connected
by a reinforcing web 8. Reinforcing web 8 is situated centrically between
first side frame 20 and third side frame 22. In addition, reinforcing web
8 is broader than an electrode, but narrower than first transverse web
60, second transverse web 61, or frame 2. Reinforcing web 8 may in
addition be fashioned as an electrode. In addition, stationary electrodes
50 and movable electrodes 51 are situated between first transverse web 60
and second transverse web 61.

[0035]Stationary electrodes 50 are connected to substrate 1, movable
electrodes 51 being connected to first side frame 20 and to third side
frame 22. Movable electrodes 51 are fashioned continuously from first
side frame 20 up to third side frame 22. In addition, movable electrodes
51 are connected to reinforcing web 8. This results in a grid-type
structure that has the advantage of a stable construction of the
acceleration sensor. However, in another specific embodiment movable
electrodes 51 may be situated so that they are not fashioned continuously
from first side frame 20 up to third side frame 22.

[0036]The electrodes are situated in such a way that two stationary
electrodes 50 are situated between each two movable electrodes 51. Here,
stationary electrodes 50 have laterally offset fastening blocks 52. The
laterally offset fastening blocks 52 are narrower than stationary
electrodes 50. This results in a small gap between stationary electrode
50 and fastening block 52. In addition, fastening block 52 is shorter in
the longitudinal direction than is stationary electrode 50. Thus, the two
fastening blocks 52 of the two stationary electrodes are centrically
situated.

[0037]In a simplified specific embodiment, the acceleration sensor has
only one spring element, one web, and one transverse web 60. Here, second
side frame 21 is connected to the web via the spring element. The web has
at least one stop element 7 that is allocated with first side frame 20
and with third side frame 22 and/or transverse web 60 as an abutment.
Stationary electrodes 50 and movable electrodes 51 are situated between
first transverse web 60 and fourth side frame 23. As in the
above-described specific embodiment, this results in a compact
construction, thus providing good stability of the acceleration sensor.

[0038]FIG. 2 shows a schematic sectional view through the acceleration
sensor along the sectional line I-I of FIG. 1. On a substrate 1 made of
silicon, first web 30 and second web 31 are raised in the form of
rectangular columns. First web 30 and second web 31 provide a solid
connection of the self-supporting structure, i.e. of frame 2, to
substrate 1. The lateral extension of the system over substrate 1 is
determined by frame 2. In the sectional view, frame 2 is represented by
second side frame 21 and fourth side frame 23.

[0039]Frame 2, transverse webs 60, 61, and spring elements 40, 41 are made
of the same material, in particular silicon. At the left part of the
representation, first web 30 is connected to second side frame 21 via a
first spring element 40. At the right area of the representation, second
web 31 is connected to fourth side frame 23 via a second spring element
41. First web 30 has first transverse web 60 on the right side. In
addition, second web 31 has second transverse web 61 on the left side.
Between first transverse web 60 and second transverse web 61, there are
situated stationary electrodes 50 and movable electrodes 51, stationary
electrodes 50 being connected to substrate 1 via fastening blocks 52.

[0040]On first transverse web 60 and second transverse web 61, and/or on
second side frame 21 and fourth side frame 23, knobs 12 may be situated
that are intended to limit the deflection of frame 2 relative to
substrate 1. The acceleration sensor can be sealed in airtight fashion by
a cap. This cap may have a bulge at certain points, acting as a
mechanical stop for the mass in the vertical direction.

[0041]First spring element 40 and second spring element 41 have different
shapes, as shown in the specific embodiments according to FIG. 3, FIG. 4,
and FIG. 5. However, these specific embodiments show only the area of
second spring element 41.

[0042]FIG. 3 shows a top view of a partial representation of a specific
embodiment of the acceleration sensor, having an S-shaped second spring
element 41. Second spring element 41 connects fourth side frame 23 to
second web 31. Second web 31 has at least one stop element 7 that is not
shown in the representation, which is allocated to first side frame 20,
to third side frame 22, and/or to second transverse web 61 as an
abutment.

[0043]Second spring element 41 is made up of three bearers 43, center
bearer 43 being twice as long as upper and lower bearers 43. In addition,
bearers 43 are situated parallel to fourth side frame 23. Upper bearer 43
is connected to second web 31 via a spring linkage 42 that abuts
centrically and perpendicular to second web 31. Lower bearer 43 is
connected to fourth side frame 23 via a spring linkage 42 that is
situated centrically and perpendicular to fourth side frame 23.

[0044]So that the etching process of the silicon is uniform, at least one
structure 9 is inserted that has no mechanical effect. Structure 9 is
intended to make the environment surrounding the structure to be etched
geometrically similar in the other areas, thus enabling a uniform removal
of the silicon by the etching process. The inserted structures 9 form the
etching environment visible in the representation. Structure 9 has small
blocks that are situated parallel to fourth side frame 23 or to second
web 31. In addition, structure 9 is situated laterally from upper or
lower bearer 43, and has the same length as bearer 43 of second spring
element 41.

[0045]FIG. 4 shows a top view of a partial representation of a specific
embodiment of the acceleration sensor, having an annular second spring
element 41. Second spring element 41 is a closed spring that connects
fourth side frame 23 to second web 31. Second spring element 41 has two
bearers 43 that are fixed to one another at their ends by spring linkages
42. In addition, bearers 43 are connected to second web 31 and to fourth
side frame 23 via two spring linkages 42 that are situated centrically
and perpendicular.

[0046]Second web 31 has at least one stop element 7 (not visible in the
drawing) that is allocated to first side frame 20, to third side frame
22, and/or to second transverse web 61 as an abutment. In addition,
second transverse web 61 is narrower than frame 2. This has the advantage
that mass can be saved.

[0047]FIG. 5 shows a top view of a partial representation of a specific
embodiment of the acceleration sensor, having a second spring element 41,
fourth side frame 23 being fashioned as second spring element 41. Fourth
side frame 23 is narrower than frame 2; in particular, it is as narrow as
second spring element 41. In addition, fourth side frame 23 is fashioned
as a bar 10, and therefore has a narrower shape than does frame 2. In
this way, bar 10 takes over the same function as second spring element
41. Bar 10 is connected to second spring element 41, as well as to a
structure 9 that forms the etching environment, via a spring linkage 42
that is situated perpendicular and centrically to bar 10. Structure 9 has
small blocks that are situated parallel to fourth side frame 23 or to
second web 31. In addition, structure 9 is situated laterally from upper
or lower bearer 43, and underneath fourth side frame 23. However,
structure 9, which is situated underneath fourth side frame 23, is
situated from first side frame 20 up to third side frame 22. Second
spring element 41 has the same shape as in the specific embodiment
according to FIG. 3.

[0048]Second web 31 has at least one stop element 7 (not shown in the
drawing) that is allocated to first side frame 20, to third side frame
22, and/or to second transverse web 61 as an abutment. Second transverse
web 61 is narrower than frame 2. This can result in a savings of mass.

[0049]FIG. 6 shows, in a simplified representation, another specific
embodiment of the acceleration sensor, in which first web 30 and second
web 31, as well as first spring element 40 and second spring element 41,
are situated outside frame 2. In addition, first spring element 40 and
second spring element 41 may have other shapes. The other elements are
fashioned as in the specific embodiment shown in FIG. 1.

[0050]It is possible for second side frame 21 and fourth side frame 23 to
be omitted. In this way, first transverse web 60, second transverse web
61, first side frame 20, and third side frame 22 form frame 2. In this
way, first spring element 40 is connected to first transverse web 60, and
second spring element 41 is connected to second transverse web 61. In
addition, first transverse web 60 and second transverse web 61 can have
knobs 12. Two stop elements 13 are situated between spring elements 40,
41 and transverse webs 60, 61; these stop elements can have additional
knobs 12. Knobs 12 of first transverse web 60 or of second transverse web
61, and knobs 12 of stop elements 13, are situated opposite one another,
and thus form paired pieces. Stop elements 13 extend into the structure
from outside, and act as mechanical stops. Stop elements 13 may have a
connecting element 14 that is connected fixedly to substrate 1 in order
to enable a stop point to be defined.